Method and apparatus for determining reverse data rate in mobile communication system

ABSTRACT

There is provided a reverse data rate determining method in a mobile communication system for high data rate transmission such as an HDR system. An AN within a cell calculates the total load of a reverse link by measuring the total energy of the reverse link from ATs within the cell. The AN calculates the share of each AT in the total reverse link load. If the load share of an AT is greater than a threshold predetermined individually for the AT, the AN determines that the AT should reduce its data rate.

PRIORITY

[0001] This application claims priority to an application entitled“Apparatus and Method for Transmitting MAC Channel in MobileCommunication System for High Data Rate Transmission” filed in theKorean Industrial Property Office on Jul. 4, 2000 and assigned Ser. No.2000-38085, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a mobile communicationsystem employing a high data rate transmission scheme, and inparticular, to a method and an apparatus for determining a reverse datarate.

[0004] 2. Description of the Related Art

[0005] Many studies have recently been made on high data ratetransmission in a CDMA (Code Division Multiple Access) mobilecommunication system. A major mobile communication system employing achannel structure for high data rate transmission is the HDR (High DataRate) system. The HDR system was proposed by the 3GPP2 (3rd GenerationPartnership Project 2) organization to reinforce data communication ofthe IS-2000 system.

[0006] A pilot channel, a forward MAC (Medium Access Control) channel, aforward traffic channel, and a forward control channel are transmittedin time division multiplexing (TDM) on a forward link in the HDR system.The set of TDM signals is called a burst. The forward traffic channeltransmits user data, and the forward control channel transmits a controlmessage and user data. The forward MAC channel transmits reverse datarate control information, reverse power control information, andinformation indicating whether forward data transmission will occur ornot.

[0007] Unlike the forward channels, reverse channels in the HDR systemare assigned to specific ATs (Access Terminals). Reverse channels foreach AT include a pilot channel, a reverse traffic channel, a reverseMAC channel, and an access channel. The reverse traffic channeltransmits user data, and the reverse MAC channel includes a DRC (DataRate Control) channel and an RRI (Reverse Rate Indicator) channel. Thereverse access channel is used to transmit a message or traffic to an AN(Access Network) before connection of a traffic channel.

[0008] A data rate control scheme and related channels in a mobilecommunication system for data transmission such as an HDR system towhich the present invention will be applied, will now be described.

[0009] To control a forward data rate, each AT transmits DRC informationin predetermined slots to an AN. The AN transmits data at a controlleddata rate only to an AT in a good channel condition. This HDRtransmission scheme remarkably increases the volume of forward link datathat can be processed. With the transmission power at a maximum, the ANtransmits more data per unit time during good channel conditions, andless data per unit time during poor channel conditions, by changing thelength. The AN transmits data to only one AT within the AN on atransmission channel for a predetermined time period. The DRCinformation provides an available forward data rate calculated based onan estimated channel state in the AT.

[0010] Unlike the forward link, the reverse link allows each AT totransmit traffic at a given data rate. Here, a maximum data rate and anoverload control scheme are also given. The AN notifies the AT of amaximum available reverse data rate through use of a ReverseRateLimit(RRL) message, and overload control information through use of an RAB(Reverse Activity Bit) on a MAC channel, both of which are transmittedin a forward slot.

[0011] The RAB is used to control a reverse data rate and thus controlreverse link overload. For example, if the RAB is 0, the AT can eitherdouble its reverse data rate or allow it to remain at its present rate .If the RAB is 1 on the AT transmits data at or above 19.2 kbps, the ATreduces its reverse data rate by one half transmits data at or above19.2 kbps.

[0012]FIG. 1 is a block diagram of a forward channel transmitter in aconventional mobile communication system employing a high data ratetransmission scheme.

[0013] Referring to FIG. 1, the forward channel transmitter in an ANtransmits a traffic channel, a preamble, a MAC channel, and a pilotchannel to an AT.

[0014] After encoded in an encoder (not shown), modulated in a modulator(not shown), and interleaved in an interleaver (not shown), the trafficchannel signal is punctured and repeated according to a data rate in asymbol puncturer & block repeater 101. A demultiplexer (DEMUX) 102demultiplexes the output of the symbol puncturer & block repeater 101.For example, the DEMUX 102 converts 16 successive bits as 16 parallelchannel signals. A Walsh spreader 103 spreads each of the 16 channelsignals by 16 Walsh codes and a channel gain controller 104 controls thegains of the spread signals. A Walsh chip level summer 105 sums theoutputs of the channel gain controller 104 at a chip level.

[0015] The preamble is repeated in accordance with the data rate in arepeater 106. A signal mapper 107 maps 0s and 1s of the output of therepeater 106 to +1s and −1s, respectively. A Walsh spreader 108 spreadsthe output of the signal mapper 107 with a predetermined Walsh code. Afirst time division multiplexer (TDM) 109 time-division-multiplexes thetraffic channel signal received from the Walsh chip level summer 105 andthe preamble signal received from the Walsh spreader 108 according to aTDM control signal. Referring to the pilot channel, 0s and 1s of thepilot channel signal are mapped to +1s and −1s, respectively, in asignal mapper 191. A multiplier 192 multiplies the output of the signalmapper 191 by a predetermined Walsh code and outputs a spread pilotchannel signal.

[0016] The forward MAC channel transmits an FAB (Forward Activity Bit),an RPC (Reverse Power Control), and an RAB. When the FAB is generated inevery frame (e.g., 26.67 ms), a bit repeater 110 repeats the FAB 15times (the FAB occurs 16 times) to increase a search probability. Forthe input of the repeated FAB symbols, a signal mapper 130 generates asignal of ±1 in a real transmission form. A multiplier 150 multipliesthe output of the signal mapper 130 by a Walsh code. The Walsh code isWalsh code #1 among Walsh codes of length 32 bits.

[0017] No power control is performed on the forward link of a mobilecommunication system like the HDR system because it transmits signalswith its maximum transmission power. However, a soft handover and apower control are required on the reverse link. Therefore, an ANtransmits the RPC bit as reverse power control information. The RPC bitis generated at 600 bps. A signal mapper 131 converts the RPC bit to asignal of ±1 in a real transmission form. A Walsh channel gaincontroller 140 multiplies the output of the signal mapper 131 by a Walshchannel gain function. The gain function applied to an RPC bit for eachAT is determined according to a DRC received from the AT. For example,if a link state is very poor, the gain controller 140 determines a gainto be 0 and transmits no power control information. A multiplier 151multiplies the output of the Walsh channel gain controller 140 by aWalsh code of length 32 corresponding to the MAC index of acorresponding AT.

[0018] A bit repeater 120 repeats the RAB according to RABLength. Thetransmission rate of the RAB is 600/RABLength bps and RABLength is knownby a channel assignment message. A signal mapper 132 converts the RAB toa signal of ±1 in a real transmission form and a multiplier 152multiplies the output of the signal mapper 132 by Walsh code #2 oflength 32.

[0019] A Walsh chip level summer 160 sums the FAB, RPC, and RAB signals.A signal repeater 170 repeats the sum three times (the sum occurs fourtimes) and multiplexes the repeated sum in the second half of a forwardtransmission slot prior to transmission to the AT. A second TDM 180time-division-multiplexes the traffic signal received from the first TDM105, the pilot signal received from the multiplier 192, and the outputof the repeater 170.

[0020]FIG. 2A illustrates the structure of an active slot in theconventional mobile communication system employing a high data ratetransmission scheme. The active slot is transmitted only when thereexists traffic or control data to be transmitted on a forward channel.

[0021] Referring to FIG. 2A, a pilot channel, a MAC channel, and trafficor control data are time-division-multiplexed in the active slot. Thepilot channel is used for channel estimation in a receiver. The pilotchannel data can be modulated in BPSK (Bi-Phase Shift Keying). The pilotchannel includes two pilot bursts per slot and each pilot burst isdisposed at the center of a half slot.

[0022] The MAC channel includes an FAB, an RPC, and an RAB. Each of thethree channels is modulated in BPSK and spread with a Walsh code oflength 32. Since each of the channels of the MAC channel is spread to 32chips and occurs four times, a total of 128 chips are assigned to theMAC channel in one slot. The 128-chip MAC channel is divided into twoequal 64-bit bursts. The two bursts are located in TDM before and afterthe second pilot burst. A traffic varies depending on channelconditions. That is, the traffic can be transmitted at a variable datarate according to the reception carrier-to-interference ratio (C/I) of areceiver and the number of slots for one can be changed according to adata rate.

[0023]FIG. 2B illustrates the structure of an idle slot in theconventional mobile communication system employing a high data ratetransmission scheme. The idle slot is transmitted when there is neithertraffic nor control data to be transmitted on the forward channel.

[0024] Referring to FIG. 2B, in the absence of forward traffic orforward control data to be transmitted, only a pilot channel and a MACchannel are transmitted in an idle slot (or an idle frame). Each idleskirt signal of all 0s is inserted before and after a first pilot burst.The idle skirt signal is transmitted to increase an accuracy with whicha reception C/I is estimated when a multi-path component of the pilotchannel arrives in the AT at a different time from that of a pilotsignal from another AN.

[0025] Only the pilot channel signal is transmitted in a first half ofthe idle slot, and the pilot channel signal and MAC channel data beforeand after the pilot channel signal are transmitted in a second halfslot. Because the arrival time of the multi-path component of the firstpilot burst differs from that of a pilot burst from another AN, thepilot bursts are at different positions on a time axis and thusinterference with the first pilot burst may be measured to be lower thanin reality. On the other hand, despite the difference between thearrival times of a multi-path component of the second pilot burst andthe pilot burst from the different AN on the time axis, the C/I isestimated accurately due to the MAC channel in the second half slot.Accordingly, the idle skirt signals are located before and after thefirst pilot burst in order to increase the accuracy of estimating theC/I of the first pilot burst. The idle skirt signals are two 64-chipbursts like the MAC channel.

[0026] Now, the FAB, RPC, and RAB of the forward MAC channel will bedescribed in detail. The FAB indicates whether a forward traffic channeland a forward control channel are activated or not on a frame by framebasis. The same FAB is transmitted in 16 slots to an AT. An FAB in annth frame indicates whether a forward channel in an (n+2) frame isactivated or not. According to the FAB, the AT can detect an AN withoutdata transmission while estimating a C/I to generate a DRC signal. Thus,the AT can set a DRC value accurately. If the FAB is 0, it implies thatthere is no data to be transmitted in the (n+2) frame and if the FAB is1, it implies that there is data to be transmitted in the (n+2) frame.

[0027] The RPC is power control information needed for reverse powercontrol. However, no power control is required on the forward linkbecause the maximum transmission power is used all the time.

[0028] The RAB is identical for all ATs, for control of data rates. Ifan RAB from at least one AN in an active set for one frame period is 1,ATs that are transmitting at or above 19.2 kbps should reduce theirreverse data rates by half. If RABs from all ANs in the active set areOs, ATs should keep their current data rates or double them. While theRAB control is advantageous in that overload is controlled by uniformcontrol of the data rates of unspecified ATs, it may result inunnecessary data rate reduction. The indiscriminate data rate control isnot appropriate when a threshold is set for RAB application and thereverse data rate of each AT is controlled according to the thresholdwhile maintaining the reverse link capacity in the vicinity of thethreshold within a controllable range of an AN.

SUMMARY OF THE INVENTION

[0029] It is, therefore, an object of the present invention to provide amethod and an apparatus for efficiently controlling overload bytransmitting an RAB on a forward MAC channel to an individual AT forimproved control of a reverse data rate in a mobile communication systemlike an HDR system.

[0030] It is another object an object of the present invention toprovide a method and an apparatus for locating a forward MAC channelseparately in the first and second half slots for efficient transmissionof the forward MAC channel in a mobile communication system like an HDRsystem.

[0031] The foregoing and other objects of the present invention areachieved by providing a reverse data rate determining method in a mobilecommunication system for high data rate transmission such as an HDRsystem. According to one aspect of the present invention, an AN within acell calculates the total load of a reverse link by measuring the totalenergy of the reverse link from ATs within the cell. The AN calculatesthe share of each AT in the total reverse link load. If the load shareof an AT is greater than a predetermined threshold, individuallyselected for the AT, the AN determines that the AT should reduce itsdata rate.

[0032] According to another aspect of the present invention, an ANwithin a cell calculates the total load of a reverse link by measuringthe total energy of the reverse link from ATs within the cell. The ANcalculates the share of each AT in the total reverse link load. If theload share of an AT is greater than a predetermined threshold for theATs, the AN determines that the AT should reduce its data rate.

[0033] According to a further aspect of the present invention, an AN ina cell calculates the total load of a reverse link by measuring thetotal energy of the reverse link from ATs within the cell. The ANcalculates the share of each AT in the total reverse link load. The ANcompares the load share of each AT with a predetermined threshold forthe AT, and determines that the AT should increase or reduce the datarate of data that the AT transmits according to the comparison result.The AN compares the reverse link capacity calculated according to thedetermined reverse data rates with the total reverse capacity of the ANand controls the thresholds according to the comparison result.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0035]FIG. 1 is a block diagram of a forward channel transmitter in aconventional mobile communication system for high data ratetransmission;

[0036]FIG. 2A illustrates the structure of a forward active slot in theconventional mobile communication system for high data ratetransmission;

[0037]FIG. 2B illustrates the structure of a forward idle slot in theconventional mobile communication system for high data ratetransmission;

[0038]FIG. 3 is a block diagram of a forward channel transmitteraccording to an embodiment of the present invention;

[0039]FIG. 4A illustrates the structure of a forward active slotaccording to the embodiment of the present invention;

[0040]FIG. 4B illustrates the structure of a forward idle slot accordingto the embodiment of the present invention;

[0041]FIG. 5 is a block diagram of a MAC channel receiver according tothe embodiment of the present invention; and

[0042]FIG. 6 is a flowchart illustrating an operation of determiningRABs for individual ATs according to the embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0043] A preferred embodiment of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

[0044]FIG. 3 is a block diagram of a forward channel transmitter thatassigns RABs individually to ATs on a MAC channel for efficient controlof data rates and overload on the reverse link in a mobile communicationsystem like an HDR system according to an embodiment of the presentinvention. In the following description, Walsh codes are used to spreadtransmission signals, but other orthogonal codes can be substituted toprovide the orthogonal spreading.

[0045] Referring to FIG. 3, the forward channel transmitter in an ANtransmits a traffic channel, a preamble, a MAC channel, and a pilotchannel to an AT.

[0046] After encoded in an encoder (not shown), modulated in a modulator(not shown), and interleaved in an interleaver (not shown), the trafficchannel signal is punctured and repeated according to a data rate in thesymbol puncturer & block repeater 101. The DEMUX 102 demultiplexes theoutput of the symbol puncturer & block repeater 101. For example, theDEMUX 102 transmits 16 successive bits as 16 parallel channel signals.The Walsh spreader 103 spreads each of the 16 channel signals by 16Walsh codes and the channel gain controller 104 controls the gains ofthe spread signals. The Walsh chip level summer 105 sums the outputs ofthe channel gain controller 104 at a chip level.

[0047] The preamble is repeated in accordance with the data rate in therepeater 106. The signal mapper 107 maps Os and Is of the output of therepeater 106 to +1s and −1s, respectively. The Walsh spreader 108spreads the output of the signal mapper 107 with a predetermined Walshcode. The first TDM 109 time-division-multiplexes the traffic channelsignal received from the Walsh chip level summer 105 and the preamblesignal received from the Walsh spreader 108 according to a TDM controlsignal. Referring to the pilot channel, 0s and 1s of the pilot channelsignal are mapped to +1s and −1s in the signal mapper 191. Themultiplier 192 multiplies the output of the signal mapper 191 by apredetermined Walsh code and outputs a spread pilot channel signal.

[0048] According to a feature of the present invention, a forward MACchannel transmitter will be described. The conventional forward MACchannel transmitter shown in FIG. 1 is so configured that it transmitsthe same RAB to all ATs indiscriminately. The RAB is spread with Walshcode #2 of length 32 such that it can be identified by any AT.

[0049] The forward MAC channel transmitter according to the presentinvention, however, multiplies an RAB by different Walsh codes accordingto MAC indexes in a multiplier 352 in order to transmit different RABsto individual ATs. Then, an AT can identify a signal destined for it byits own MAC index. In connection to an HDR service session, the ANassigns a UATI (Unicast Access Terminal Identifier) of 32 bits. The ANalso assigns a MAC index to an AT that enters the service area of eachsector. Each MAC index is assigned 5 bits, included in a channelassignment message transmitted for assignment of a dedicated channel.Since a different Walsh code is assigned to each MAC index, an AT candetect only its own information by the MAC index. RAB processing issimilar to modulation/demodulation of an RPC for control of reversetransmission power for an individual AT.

[0050] In FIG. 3, an RPC and an FAB/RAB are transmitted in differenthalf slots. The RPC is converted to a signal of ±1 in a realtransmission form by the signal mapper 131. The Walsh channel gaincontroller 140 multiplies the output of the signal mapper 131 by a gainfor a corresponding AT. The gain is determined according to a DRCreceived from the AT. The multiplier 151 multiplies the output of theWalsh channel gain controller 140 by a Walsh code for the AT, forspreading. A Walsh chip summer 350 sums RPCs for ATs received from themultiplier 151. A signal repeater 370 repeats the output of the Walshchip summer 350 predetermined times (e.g., three times) and outputs therepeated symbols such that the RPC signal is inserted before and afterthe second pilot burst. The operation of the signal repeater 370 iscontrolled according to a slot division control signal received from acontroller 380. The second TDM 180 time-division-multiplexes the RPCsignals received from the repeater 370 with other signals (the pilotchannel signal and the traffic channel data).

[0051] An RAB is generated by an RAB generator 390. The RAB generator390 performs an operation of determining and generating an RAB for eachAT, which is illustrated in the following FIG. 6. It is noted that thedetailed operation of the RAB generator 390 will be described withreference to FIG. 6. The bit repeater 120 repeats the RAB according toRABLength. The signal mapper 132 converts the RAB to a signal of ±1 in areal transmission form and a channel gain controller 340 multiplies theRAB signal received from the signal mapper 132 by a gain for the AT. Amultiplier 352 multiplies the output of the gain controller 340 by aWalsh code for the AT, for spreading.

[0052] An FAB is repeated by the bit repeater 110. For the input of therepeated FAB signal, the signal mapper 130 generates a signal of ±1 in areal transmission form. The multiplier 150 multiplies the output of thesignal mapper 132 by Walsh code #1 of length 32.

[0053] A Walsh chip level summer 360 sums the FAB signal received fromthe multiplier 150 and the RAB signals for the ATs received from themultiplier 352. A signal repeater 371 repeats the sum predeterminedtimes (e.g., three times) so that the RAB/FAB signal is inserted beforeand after the first pilot burst in the first half slot. The operation ofthe signal repeater 371 is controlled according to a slot divisioncontrol signal received from the controller 380. The RAB/FAB signals aremultiplexed with other signals (the pilot channel signal and the trafficchannel data) by the second TDM 180.

[0054] As stated above, the signal repeaters 370 and 371 operateaccording to the slot division control signals received from thecontroller 380. In other words, the controller 380 generates the slotdivision control signal so that the signal repeater 370 operates in thesecond half slot and the signal repeater 371 operates in the first halfslot.

[0055] In the case of an active slot, the second TDM 180 generates aslot as shown in FIG. 4A with the traffic channel data, the pilotchannel signal, the RAB/FAB, and the RPC according to a TDM controlsignal from the controller 380. In the case of an idle slot, the secondTDM 180 generates a slot as shown in FIG. 4B with the pilot channelsignal, the RAB/FAB, and the RPC according to the TDM control signalfrom the controller 380. Since the RAB/FAB and the RPC are output fromthe repeaters 370 and 371 in accordance with timing shown in FIG. 4A or4B, the second TDM 180 merely multiplexes the RAB/FAB and the RPC to beinserted before and after the pilot bursts.

[0056]FIG. 4A illustrates the structure of an active slot according tothe embodiment of the present invention. An FAB and an RAB for anindividual AT are transmitted in the first half slot and an RPC for theindividual AT in the second half slot. The forward MAC channel istransmitted before and after each pilot burst separately in the firstand second half slots.

[0057] The conventional forward channel transmitter shown in FIG. 1transmits the sum of a FAB, an RAB, and an RPC in the second half of aforward transmission slot. However, since RABs are spread with 32 Walshcodes with the MAC indexes of ATs used as the IDs of the ATs in thepresent invention, transmission of an RAB with the RPC in the secondhalf slot will make it impossible to discriminate between the RAB andthe RPC. Therefore, the RAB is transmitted in the first half slot andthe RPC in the second half slot.

[0058] In the case where the same power is consumed, it makes nodifference whether the FAB is located in the first half slot or in thesecond half slot. The RAB can be transmitted with a less error ratebecause it occurs repeatedly in 8 to 24 slots, whereas the same RPCoccurs once in one slot and thus with a higher error rate. Therefore,the FAB is transmitted with the RAB in the first half slot in theembodiment of the present invention.

[0059]FIG. 4B illustrates the structure of an idle slot according to theembodiment of the present invention. The FAB/RAB of the forward MACchannel is transmitted separately in the first half slot.

[0060] Referring to FIG. 4B, MAC channel signals are transmitted insteadof the idle skirt signals in the conventional idle slot shown in FIG.2B. The RAB/FAB signal and the RPC signal, that are spread with Walshcodes of length 32 and repeated three times, are transmitted in the twoskirt bursts of the first half slot. As stated before, the FAB is spreadwith Walsh code #1 of length 32, while the RAB and RPC are multiplied bya corresponding MAC index other than Walsh codes #0 and #1. The FAB, theRPC, and the RAB are summed at a chip level before transmission as MACchannel data. Regardless of an active slot or an idle slot, the MACchannel data is transmitted by 64 chips before and after the pilot burstin both the first and second half slots. The RAB/FAB is before and afterthe pilot burst in the first half slot and the RPC is before and afterthe pilot burst in the second half slot.

[0061]FIG. 5 is a block diagram of a receiver in an AT for receiving aforward MAC channel according to the embodiment of the presentinvention. Referring to FIG. 5, a complex despreader 510complex-despreads a received signal and a channel compensator 520channel-compensates the despread signal. A DEMUX 550 demultiplexes thechannel-compensated signal into traffic data and MAC channel data in thereverse order of TDM in the TDM 180 of the forward channel transmitteraccording to a TDM signal received from a controller 560.

[0062] A symbol combiner 530 combines the traffic symbols of the DEMUX550 and outputs the combined traffic signal as traffic channel data. Asymbol combiner 531 adds repeated symbol energy to the MAC channel datain the second half slot and a multiplier 541 multiplies the resultingMAC channel data by a Walsh code corresponding to the MAC index of theuser. Thus, an RPC for the AT is separately detected.

[0063] A symbol combiner 532 adds repeated symbol energy to the MACchannel data in the first half slot and multipliers 540 and 542 multiplythe resulting MAC channel data by Walsh code #1 and the Walsh codecorresponding to the MAC index of the user, respectively. Thus, an FABand an RAB for the AT are separately detected.

[0064] More specifically, a 128-chip MAC channel signal in each halfslot is accumulated by 32 chips, four times, in a symbol combiner, andthus a 32-chip MAC signal is generated. The multiplier 540 recovers theFAB by multiplying the 32-chip MAC signal received from the symbolcombiner 532 by Walsh code #1 of length 32 and the multiplier 542recovers the RAB by multiplying the 32-chip MAC signal received from thesymbol combiner 532 by the MAC index. The multiplier 541 recovers theRPC by multiplying the 32-chip MAC signal received from the symbolcombiner 531 by the MAC index. The multipliers 540, 541, and 542 act asdespreaders for outputting despread MAC channel signals.

[0065]FIG. 6 is a flowchart illustrating an operation of determining anRAB for each AT to transmit different RABs to different ATs according tothe embodiment of the present invention. By this procedure, an AN cancontrol overload. Referring to FIG. 6, the AN measures the total load Ton the reverse link by measuring the total energy of the reverse linkfrom the ATs in a sector in step 610. Here,$T = {\sum\limits_{i = 1}^{N}{{REV}\quad \_ \quad {{{LOAD}_{i}(t)}.{REV}}\quad \_ \quad {{LOAD}_{i}(t)}}}$

[0066] is a parameter indicating the load imposed on the reverse link byan ith AT. The AN can determine the reverse load REV_LOAD proportionallyby calculating the reception energy of a signal from each AT. Thereception energy includes energy related with the volume of receiveddata and interference from adjacent cells, and thermal noise energy.$\begin{matrix}\begin{matrix}{{{REV}\quad \_ \quad {{LOAD}_{i}(t)}} = {\int_{i - D}^{t}{\left\lbrack {r_{i}(\tau)} \right\rbrack^{2}{\tau}}}} \\{= {\int_{t - D}^{t}{\left\lbrack {{r(\tau)}{{pn}_{i}(\tau)}} \right\rbrack^{2}{\tau}}}}\end{matrix} & (1)\end{matrix}$

[0067] where D is a measuring time period, r_(i) is a signal receivedfrom the ith AT, r is signals received from ATs, and pn_(i) is the PNcode of the ith AT.

[0068] In step 620, the AN calculates the share of each AT in the totalreverse load. The share of each AT is calculated by comparing the totalreverse load with the load of each AT measured for a predetermined timein E_(i)(t)=REV_LOAD_(i)(t)/T. A variable indicating the number k of ATsis set to an initial value, 0 in step 630.

[0069] In step 640, a predetermined value α×TH_(i) is compared with theload measurement E_(i) in order to determine an RAB for each AT. Thevariable α can be varied according to the comparison result between thetotal reverse link capacity and the measured reverse link capacityduring the RAB determination procedure for each AT. α is less than 1 andcan be initially determined considering the number N of the ATs in thecell. For example, if N is less than a predetermined threshold N_TH, αcan be set to a small value in order to increase the number of ATs whichcan increase their data rates. On the contrary, if N is greater thanN_TH, α can be set to a large value in order to reduce the number of ATswhich can increase their data rates.

[0070] The threshold TH_(i) can be set to a different value for each ATaccording to a service connected to the AT and the class of the AT. Orthe threshold TH_(i) can be identical for all ATs. If the load of the ATis greater than the predetermined value in step 640, the procedure goesto step 650, and otherwise, the procedure goes to step 651. In step 650,an RAB for the AT is set to 1 and in step 651, it is set to 0. If theRAB is 1, the AT is supposed to reduce its data rate, for example, byhalf. If the RAB is 0, the AT is supposed to increase the reverse datarate, for example, by two fold. The RAB determination in steps 640 and650 or 651 is performed until it is checked whether RABs are determinedfor all the ATs in step 660. In step 655, k is increased by 1. It isdetermined whether k is equal to N in step 660. If they are equal, thatis, RABs are determined for all the ATs, the RABs are transmitted to theATs in step 670.

[0071] Meanwhile, steps 680, 690, and 695 are performed before an RAB isdetermined for another AT. In step 680, the reverse capacity TOT_Tk isupdated. The total receivable reverse capacity T_TH of the AN iscompared with the updated reverse capacity TOT_Tk in step 690, and thevariable α (<1) is adjusted according to the comparison result in step695. For example, as the updated reverse capacity approaches to thetotal reverse capacity, the variable α is adjusted to be less, tothereby increase the number of ATs that can increase their data rates.

[0072] The above RAB determination procedure is performed for all ATswithin a cell and in the following order according to the embodiment ofthe present invention.

[0073] (1) An AN determines ATs requesting a predetermined data rate;

[0074] (2) The AN checks the service priorities of the ATs;

[0075] (3) The AN determines RABs for the ATs in a descending order ofthe service priorities;

[0076] (4) If there are ATs that have the same priority, the ANdetermines an RAB first for an AT with a lower data rate; and

[0077] (5) The AN gives a lower priority to an AT having a high priorityfor more than a predetermined number times to maintain service equitybetween ATs.

[0078] If services are completely provided to the ATs requesting thepredetermined data rate, RABs are determined for ATs with lower currentdata rates and higher priorities among ATs in services to which timedelay is not so important. A lower priority is given to an AT having ahigh priority for more than a predetermined number times in the nextdata rate determination procedure.

[0079] As described above, the present invention provides a method andan apparatus for transmitting an RAB to an individual AT on a forwardMAC channel and a modified forward transmission slot, for control ofreverse data rate. While the existing HDR system has limitations ineffective overload control due to indiscriminate reverse data ratecontrol for all ATs, an individual AT-based reverse data rate isperformed in the present invention, thereby achieving efficient overloadcontrol and preventing drastic data rate changes in ATs. Furthermore,the AT-based data rate control of the present invention is moreacceptable for supporting services of diverse characteristics orcontrolling data transmission according to user classes.

[0080] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method of controlling reverse data rates in amobile communication system having an AN (Accesss Network) and aplurality of ATs (Acess Terminals) in one cell, comprising the steps of:calculating a total load of a reverse link by measuring a total energyof the reverse link; calculating a load share of each AT in the totalreverse link load; and considering each of the plurality of ATs anddetermining that an AT reduce the reverse data rate when the load shareof the AT is greater than a predetermined threshold individuallyselected for the AT.
 2. The method of claim 1, further comprising thestep of considering each of the plurality of ATs and determining that anAT increase the reverse data rate when the load share of the AT is lessthan or equal to the predetermined threshold.
 3. The method of claim 1,wherein the plurality of ATs are considered in an ascending order of thereverse data rates of the plurality of ATs.
 4. The method of claim 1,wherein the plurality of ATs are considered in a descending order of theservice priorities of the plurality of ATs.
 5. The method of claim 1,wherein the total energy includes energy included in the volume of datareceived from the plurality of ATs.
 6. The method of claim 1, whereinthe total energy includes energy from interference from adjacent cells.7. The method of claim 1, wherein the total energy includes energy fromthermal noise.
 8. A method of controlling reverse data rates in a mobilecommunication system having an AN (Access Network) and a plurality ofATs (Access Terminlas) in one cell, comprising the steps of: calculatinga total load of a reverse link by measuring a total energy of thereverse link; calculating a load share of each AT in the total reverselink load; and considering each of the plurality of ATs and determiningthat an AT reduce the reverse data rate when the load share of the AT isgreater than a predetermined threshold for the AT.
 9. The method ofclaim 8, further comprising the step of considering each of theplurality of ATs and determining that an AT increase the data rate ofdata that the AT transmits when the load share of the AT is less than orequal to the predetermined threshold.
 10. The method of claim 8, whereinthe plurality of ATs are considered in an ascending order of the reversedata rates of the plurality of ATs.
 11. The method of claim 8, whereinthe plurality of ATs are considered in a descending order of the servicepriorities of the plurality of ATs.
 12. The method of claim 8, whereinthe total energy includes energy included in the volume of data receivedfrom the plurality of ATs.
 13. The method of claim 8, wherein the totalenergy includes energy from interference from adjacent cells.
 14. Themethod of claim 8, wherein the total energy includes energy from thermalnoise.
 15. A method of controlling reverse data rates in a mobilecommunication system having an AN (Access Network) and a plurality ofATs (Access Terminals) in one cell, comprising the steps of: calculatinga total load of a reverse link by measuring a total energy of thereverse link; calculating a load share of each AT in the total reverselink load; comparing the load share of each AT with a predeterminedthreshold for the AT, and determining that the AT adjust the reversedata rate according to the comparison result; and comparing the totalload of the reverse link calculated with the total reverse capacity ofthe AN and controlling the thresholds according to the comparisonresult.
 16. The method of claim 15, wherein the step of comparing theload share of each AT and determining that the AT adjust the reversedata rate comprises the steps of: decreasing the reverse data rate whenthe load share of the AT is greater than the predetermined threshold forthe AT; and increasing the reverse data rate of when the load share ofthe AT is less than or equal to the predetermined threshold for the AT.17. The method of claim 15, wherein the step of comparing the load shareof each AT and determining that the AT adjust the reverse data rate isperformed in an ascending order of the reverse data rates of the ATs.18. The method of claim 15, wherein the step of comparing the load shareof each AT and determining that the AT adjust the reverse data rate isperformed in a descending order of the service priorities of the ATs.19. The method of claim 18, wherein a low service priority is given toan AT having a high service priority more than predetermined times. 20.The method of claim 15, wherein the total energy includes energyincluded in the volume of data received from the ATs.
 21. The method ofclaim 15, wherein the total energy includes energy from interferencefrom adjacent cells.
 22. The method of claim 15, wherein the totalenergy includes energy from thermal noise.
 23. The method of claim 15,wherein the thresholds are determined separately for each AT.
 24. Themethod of claim 23, wherein the thresholds are multiplied by a variablehaving a value less than
 1. 25. The method of claim 24, wherein thevariable is adjusted as a function of adjustment to the thresholds. 26.The method of claim 24, wherein as the reverse link capacity for the ANapproaches the total reverse capacity, the variable is decreased. 27.The method of claim 24, wherein the initial value of the variable is afunction of the number of ATs within the cell.
 28. The method of claim27, wherein the initial value of the variable is set to a large value ifthe number of the ATs is greater than a predetermined number.
 29. Themethod of claim 27, wherein the initial value of the variable is set toa small value if the number of the ATs is less than a predeterminednumber.
 30. An access network (AN) in a cell for controlling reversedata rates for a plurality of ATs (Access Terminals) in a mobilecommunication system, comprising: a data rate information generator forcalculating a total load of a reverse link by measuring a total energyof the reverse link from the ATs, comparing a share of each AT in thetotal reverse link load with a predetermined threshold for the AT, andgenerating data rate information for the AT to control the data rate ofthe AT according to the comparison result; and a transmitter fortransmitting the generated data rate information to the AT.
 31. The ANof claim 30, wherein the transmitter comprises a spreader for spreadingthe data rate information with an orthogonal code predetermined for theAT.
 32. The AN of claim 30, wherein the data rate information generatorcompares the capacity of the reverse link calculated based on thedetermined data rate with the total reverse capacity of the AN andcontrolling the threshold according to the comparison result.
 33. The ANof claim 30, wherein the data rate information generator reduces thereverse data rate when the load share of the AT is greater than thethreshold, and increases the reverse data rate when the load share isless than or equal to the threshold.
 34. The AN of claim 30, wherein thedata rate information generator generates data rate information in anascending order of the reverse data rates of the ATs.
 35. The AN ofclaim 30, wherein the data rate information generator generates datarate information in a descending order of the service priorities of theATs.
 36. The AN of claim 35, wherein the data rate information generatorassigns a low service priority to an AT having a high service prioritygreater than a predetermined number of times.
 37. The AN of claim 30,wherein the total energy includes energy related to the volume of datareceived from the ATs.
 38. The AN of claim 30, wherein the total energyincludes energy related to interference from adjacent cells.
 39. The ANof claim 30, wherein the total energy includes energy related to thermalnoise.
 40. The AN of claim 30, wherein a different threshold is set foreach AT.
 41. The AN of claim 40, wherein the threshold is multiplied bya variable less than
 1. 42. The AN of claim 41, wherein the variable isadjusted as a function for controlling the threshold.
 43. The AN ofclaim 41, wherein as the reverse link capacity for the AN approaches thetotal reverse capacity, the variable is decreased.
 44. The AN of claim41, wherein the initial value of the variable is a function of thenumber of the ATs within the cell.
 45. The AN of claim 44, wherein theinitial value of the variable is set to a large value if the number ofthe ATs is greater than a predetermined number.
 46. The AN of claim 44,wherein the initial value of the variable is set to a small value if thenumber of the ATs is less than a predetermined number.